No, you didn’t. Here, I’ll help you out -
“Includes everything in the Base Edition, plus instant access to a Level 120 Character Boost and the Ensorcelled Everwyrm flying mount. The flying mount grants a quest for the Vestments of the Eternal Traveler transmog set.”
That’s the description for the heroic pre-purchase. Let’s dig deeper into the description…
“The flying mount grants a quest for the Vestments of the Eternal Traveler transmog set.”
So, basically, you get access to a quest, upon completion of the quest you’ll be granted the set.
Crazy, I know.